High intensity discharge (HID) lights produce light by generating an electric arc across two spaced-apart electrodes housed inside a sealed quartz or alumina arc tube filled with gas or a mixture of gas and metals. The lamps of some HID lights include a third electrode within the arc tube that initiates the arc when the lamp is first lit. Other lights use a starting circuit referred to as an igniter, in place of the third electrode, that generates a high-voltage pulse to the electrodes to start the arc. Initially, the amount of current required to heat and excite the gases in the arc tube is high. Once the chemistry inside the arc tube reaches its “steady-state” operating condition, much less power is required. Since HID lights are negative resistance devices, they require an electrical ballast to provide a positive resistance or reactance that regulates the arc current flow and delivers the proper voltage to the arc during start-up and operation. The ballast is powered by a battery that is connected to the ballast.
U.S. Pat. No. 5,630,661, issued to Fox, illustrates a rechargeable metal arc flashlight with a battery that is connected to the ballast through multiple springs that appear to be part of the battery housing. U.S. Pat. No. 5,604,406 illustrates a portable metal halide light with three spring loaded contacts within the battery housing that transfer power from a power source to the flashlight's circuit board. U.S. Pat. Nos. 6,702,452, 6,896,392 and 6,909,250, all issued to Jigamian et al. (“Jigamian Patents”), illustrate a xenon arc search light with a field replaceable battery, but while it is stated that the battery can be removed from the rear of the lamp, no indication is given as to how the battery connects to the connectors that engage the lamp.
HID lights are ideal for lighting applications that require a beam of light that can travel great lengths to clearly illuminate distant objects, such as search lights, targeting lights, flash lights and other security, rescue, police and military applications. HID lights can also be useful in police and military applications. A HID light that produces infrared light is also useful in covert military operations, in cooperation with night vision goggles, to allow military personnel to see without being seen.
HID lights used in military and similar types of applications require a number of special features that are essential to the utility of the light and the safety of the light's user. Such lights need to be rugged and capable of withstanding sharp blows (as might occur when the lamp is dropped or used in hand-to-hand combat operations) and many different atmospheric conditions (fog, wind, water, dust, high heat and cold, etc.). The lamp and the battery need to be field replaceable, meaning that they can be easily swapped out in the field, without compromising the light, by a user, should the lamp break or a battery run too low on power. The light needs to be able to provide a number of different sources of light to fit appropriate circumstances. For example, the amount of light provided by the main lamp might be appropriate to illuminate a target, but would be inappropriate for use in reading a map.
The light also needs to be able to provide an early warning to a user that a battery is running low, so the light does not stop working at a bad time, i.e., during combat. While battery life indicators are known in handheld lights, such as that illustrated by U.S. Pat. No. 4,876,632, issued to Osterhout et al., a series of shining LED lights on the exterior of the housing are not always desirable, especially in covert operations.